Late Pleistocene Shoreline Fluctuations of Lake Manix, Mojave Desert: Paleoclimate Implications
Marith C. Reheis, David M. Miller, and John P. McGeehin Regional setting of Lake Manix
Lake Thompson Why study the Mojave?
¾Presently occupies a transition zone between areas dominated by westerly Pacific winter moisture and southerly monsoon summer moisture ¾Terrestrial climate proxies may record changing influence of these moisture sources Jet stream D-O cycles H events ? PDO ENSO NAM, PNA…..? Mojave River fed Lake Manix between about 500 ka and 25 ka; occasionally, river diverted to Harper Lake
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y a
d b
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u C
543 m (in blue), controlled by s ≤ Late P highstands were threshold near Afton Canyon and internal sill to Coyote Lake 14 C dating sites (Anodonta shells) Each dot typically represents multiple dates / sites Calibrated using Fairbanks et al. conversion Late Quaternary lake phases
Lake 8 (MIS 3): Mostly shallow- water sand and gravel preserved
Lake 7 (MIS 6-4?): Mostly deeper-water green mud interbedded with sand at line Tufa-co
Tufa-coated clasts commonly mark lake transgressions in gravelly sediment Upper Dunn Wash— fluvio-lacustrine deposits
Tufa-coat lines Buried soil
36.8 ka
40.1 ka Upper Lake 8 Dunn Wash sections Lake 7 Other selected sections east west Coyote Lake dating sites
543 m barrier beach
35535 36690 31700 46800
33640 35220
27030
Post-Manix (25 ka) river and lake deposits SE Lake Coyote: stratigraphy & interpretation
M08SM-940 Many rapid fluctuations indicated by ostracode-hash “death beds”
Shell bed 36.7 cal ka
M07SM-2448
Shell bed 33.6 cal ka
Buried soil vaguely laminated gypsic sand
fine and med sand, rippled with 30.1 14Ckyr mud drapes in upper 4 cm
hard mud and vfi sand, ripple laminated
14 loose med sand, well sorted, 38.4 Ckyr laminated hard blocky mud; floating sand grains; one shell layer; one thin sand in middle. Soil? loose medium sand, faintly laminated
mud with lenses and v. thin beds of sand, some rippled SE Coyote Lake—hand dug pit plus outcrop
¾Thin sedimentary packages ¾Small-scale stratigraphy reveals complex record ¾Three main lake phases separated by exposure and soil formation Hiatus / soil fm. Provisional lake-level curve Other events affecting lake level
Spilling into/ out of Coyote lake Coyote sill altitude
Afton Canyon cut
Diversion to Harper L? Comparison to other Great Basin lakes Comparison to other records
H4
H3
H2 Conclusions
¾ High-resolution MIS 3 record ¾ Lake Manix very sensitive to climate/runoff ¾ Broad features of record (but not all details) most similar to far southwest lakes: Babicora, Baldwin ¾ MIS-3 lake levels correspond to SOME events in marine / ice records: ¾ Low levels during H4 and H3; H2 occurred during cutting of Afton Canyon ¾ Some high levels match D-O (warm) events—but major highstands at ~30 and 25 ka do not Helpful ideas will be appreciated!